1. Field of the Invention
The present invention relates to a magnetoresistive element.
2. Description of the Related Art
A multilayer film with a basic configuration of ferromagnetic layer/non-magnetic layer/ferromagnetic layer is known to provide a magnetoresistance effect (MR effect) by allowing a current to flow across the non-magnetic layer that is an intermediate layer. The MR effect depends on the magnitude of a relative angle between the magnetization directions of the ferromagnetic layers sandwiching the non-magnetic layer. A magnetoresistive element (MR element) that includes a non-magnetic layer made of an insulating material is referred to as a TMR element. An MR element that includes a non-magnetic layer made of a conductive material (e.g., Cu) is referred to as a GMR element. Another type of GMR element allows a current to flow parallel to the plane of the lamination. The MR element can be used, e.g., in a magnetic head for a magnetic recording medium or a device such as a magnetic memory (MRAM).
There has been progress in miniaturization of the MR element to achieve a high-density magnetic head or MRAM, which in turn increases a demand for MR elements that can provide a larger rate of change in magnetoresistance (MR ratio) or higher output. For this purpose, it is important to control the composition of a multilayer film of the MR element on the order of nm. When the MR element is used in a device, particularly in MRAM or the like, a monolithic structure combining the MR element and a general Si semiconductor is essential in view of the cost and the degree of integration. This monolithic process involves heat treatment at high temperatures to remove wiring defects or the like. Therefore, the MR element is required to have excellent heat resistance. For example, the heat treatment to remove wiring defects of the Si semiconductor should be performed in a hydrogen atmosphere at a high temperature of 400° C. to 450° C.
However, the magnetoresistance characteristics (MR characteristics) of a conventional MR element are likely to be degraded under heat treatment at about 300° C. to 350° C. Even if the conventional MR element has high heat resistance, such degradation occurs at 300° C. to 380° C. or more (see, e.g., Journal of Applied Physics, vol. 89, No. 11, p6665, Journal of the Magnetics Society of Japan, vol. 25, No. 4-2, pp.775-778(2001), Amano et al., or the documents of the 116th Symposium of the Magnetics Society of Japan, p16).
To avoid the degradation of the MR characteristics by heat treatment, a method for incorporating MR elements after the formation of semiconductor elements has been proposed (see, e.g., the documents of the 112th Symposium of the Magnetics Society of Japan, p 41). In this method, however, wiring between the MR elements, wiring between the MR elements and the semiconductor elements, or wiring for applying a magnetic field to the MR elements should be formed after producing the MR elements. Therefore, if the heat treatment for removal of wiring defects is not performed, a wiring resistance may vary and thus degrade the reliability and stability of the elements.
Alternatively, the heat treatment temperature may be decreased so as not to degrade the MR characteristics of an MR element, while the output of the MR element may be increased, thereby suppressing wiring variations due to wiring defects. In this case, it is preferable to use the element that can provide as large an MR ratio as possible.